The affect heuristic is a heuristic in which current affect influences decisions. The emotion your in influences your decision making and judgement.
Emotions (subconsciously) influence our actions. You can use this to stimulate certain behavior. You can use your websites copy, images or design te evoke certain emotions te elicit feelings such as humor or pleasure.
Recently I've seen some (often absolute) statements going around, generally in the line of "open source commerce platforms are a terrible idea". Now of course different solutions always have different pros and cons.
A hierarchy of evidence (or levels of evidence) is a heuristic used to rank the relative strength of results obtained from scientific research. I've created a version of this chart/pyramid applied to CRO which you can see below. It contains the options we have as optimizers and tools and methods we often use to gather data.